add `extra_repr` for `nn.ZeroPad2d` (#69206)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/69205
Pull Request resolved: https://github.com/pytorch/pytorch/pull/69206
Reviewed By: H-Huang
Differential Revision: D32759597
Pulled By: jbschlosser
fbshipit-source-id: abc9ee69fb5e22d45a640993a4e598b016020688
